Attempts to deal with trapped air and/or these volatile products of the moulding process by enclosing the moulding tool in a box constituted by sliding and pivoting sidewalls have been only moderately satisfactory, mainly due to their complexity and to premature failure of the necessary resilient seals.
Compression moulding presses are well-known in the moulding art and can be divided in very general terms into two classes, although their principle of operation is essentially the same. A rigid supporting framework incorporates a fixed platen and a moving platen which is displaceable towards and away from the fixed platen for example by means of a hydraulic ram or screw jack. The two platens are adapted to each carry one half of a moulding tool, the arrangement being such that displacement of the moving platen towards the fixed platen brings together the moulding tool halves so as to define a moulding cavity between them.
The moving platen is usually arranged to move in a vertical path; the means for displacing it relative to the fixed platen may be above the moving platen, in which case the press is of the downstroking class, or it may be below the moving platen, in which case the press is of the upstroking class. The present invention can be adapted to either class of press. Examples of upstroking presses are found in U.S. Pat. Nos. 3,997,286 and 2,542,874. Downstroking presses are generally similar, but have the platen means displacing at the top of the framework, the fixed platen being therefore in the position occupied by the main ram assembly shown in the two patents just referred to.